Abstract:
This project began in 1971 at a tropical site that was once natural forest. The soil is described as a Beni silty clay loam series of fine loamy mixed hyperthermic family of Aquic Hapludoll (USDA).

Time zero soil measurements taken. Details of soil sampling method: Initial composite sample was collected from 0-20cm with a spade. After the layout of the experiment, 10-12 cores from each plot were sampled using stainless steel tube auger for rice and a stainless steel auger for wheat and cowpea crops in a zig-zag as described by Jackson (1973) Soil Chemical Analysis. Printice-Hall of India Pvt Ltd., New Delhi, India. Subsequently, similar composite samples were drawn from each plot after each crop/annual cropping cycle. Soil is separated into layers. Details of measuring depths and soil layers: 0-15, 15-30, 30-60 and 60-90 cm after 15 and 20 annual cropping cycles (rice-wheat-cowpea fodder).

c) Soil measurements made and frequency

Total carbon: After each crop/cropping cycle Method of measuring total carbon: Walkley-Black method (Walkley and Black , 1934, Soil Sci. 37: 29-38). Total nitrogen: Measurements made; frequency not specified Method of measuring total nitrogen: Modified Kjeldahl method as described in Jackson, M.L. (1973) Soil Chemical Analysis. Printice-Hall of India Pvt Ltd., New Delhi, India. Total mineral nitrogen: After each cropping cycle Method of measuring total mineral nitrogen: Available soil nitrogen measured as described in Subbiah, B.V. and Asija, G.L. (1956) A rapid procedurefor the estimation of available N in soils. Current Science 25: 259-260. Nitrate nitrogen: Measurements made; frequency not specified. Method of measuring nitrate nitrogen: Method no specified. Soil bulk density or weight: Measured but frequency not specified. Other nutrients: Available N, P, K, S, Zn, Fe, Mn, Cu etc. Other measurements: Some measurements of soil enzymes have been made.

Description:
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There are at least 4 replicates in the experiment. The experiment has a randomized plot design. Bulk crop ... rice was grown in 2-3 seasons before laying out of the experiment after selection of the site. Based on the fertility gradient (as far as possible), replications were assigned in such a way that all the treatments in one replication had more or less uniform fertility status. The treatments in each replication were allotted at random from random number tables in standard statistics textbook.

There are absolute control plots (nil inputs), fallow plot; various treatments serve as controls for others.